1. Field of the Invention
The present invention relates to an apparatus for wet thermal oxidation of a semiconductor specimen, used in a compound semiconductor fabrication process.
2. Description of the Related Art
Various systems and apparatuses for oxidizing a specimen in a compound semiconductor fabrication process have been suggested. A typical oxidation apparatus is shown in FIG. 1, which uses an open-type oxidation system in which external gas continuously flows in.
That is, referring to the drawing, the open-type system oxidation apparatus includes a tank 10 containing water, a heating furnace installed encompassing the tank 10 to heat the water in the tank 10, a pipe 12 through which vapor generated by heating the water in the tank 10 flows, a chamber 14 where a specimen 100 is located, a holder 15 installed at the chamber 14 for supporting the specimen 100, and a discharge pipe 17 through which the vapor is discharged. Also, valves 18 are installed at the pipe 12, if necessary. A heating furnace 16 for heating the chamber 14 is installed adjacent to the chamber 14.
In the present apparatus, nitrogen N.sub.2 is used as a carrier gas to carry the vapor generated in the tank 10. The nitrogen flows in the pipe 12 and the amount of flow is appropriately controlled by a flow controller 13.
In the operation of the conventional oxidation apparatus having the above structure, first, the heating furnaces 11 and 16 are driven to heat the tank 10 containing water and the chamber 14 where the specimen 100 subject to oxidation is placed. Here, the tank 10 is heated to a temperature between 80.degree. C. and 100.degree. C. to generate vapor and the chamber 14 is heated to a temperature between 350.degree. C. and 500.degree. C. When the tank 10 and the chamber 14 are heated to appropriate temperatures, the specimen 100 supported by a holder 15 is placed in the chamber 14.
Next, as the amount of nitrogen flowing in is controlled by the flow controller 13, the nitrogen flows in the chamber 14 along with the vapor generated in the tank 10 and flows through the pipe 12 so that oxidation of the specimen 100 begins.
As the external nitrogen and vapor continuously flows in the chamber 14 in the oxidation apparatus adopting the open-type system, the oxidation atmosphere in the chamber 14 is barely maintained in a constant state due to change in the external circumstances. Also, when the nitrogen gas is horizontally provided with respect to the specimen 100, as the nitrogen gas is gradually heated while proceeding due to the high temperature in the chamber 14, the temperature of the nitrogen gas located at the position far away from an end portion of the pipe 12 through which the nitrogen gas is provided is higher than that of the nitrogen gas near the end portion of the pipe 12. The unevenness of the temperature of the nitrogen gas consequently serves as a hindrance to uniform oxidation throughout the specimen 100. Such tendency becomes severe as the length of the specimen 100 increases. Thus, uniformity at oxidation is lowered.
Further, vapor is condensed at an inner wall of the pipe 12 where the vapor flows and water drops are formed. The water drops are expelled into the chamber 14 by a gas such as nitrogen so that the specimen 100 may be wet, which lowers reliability and representation of a compound semiconductor specimen.
The above problem also occurs when the pipe 12 is installed perpendicular to the specimen 100 in the chamber 14. Thus, the specimen wetting phenomenon due to water drops occurs more frequently.